Season 4 of Blue Bloods has begun and the cast has been tweeting from set and live tweeting broadcasts. Check out tweets and pics from Donnie Wahlberg, Sami Gayle and Amy Carlson, with a special tribute to birthday boy Len Cariou!

Seriously?!?! 14.5 million viewers on a Friday night at 10PM!!!! #BLUEBLOODS continues to defy the odds!!